For the last few years, consumers have been told that 4G is coming, but multiple setbacks caused by the global economic downturn and delays to the 4G spectrum auction have meant that it is still not available in the UK. As a result, the UK now ranks behind 34 countries worldwide that have already launched 4G services.
Fortunately, the future for 4G is starting to look brighter – Ofcom has recently announced that it plans to hold the 4G spectrum auction early next year. However, spectrum availability is not the only issue that mobile operators must overcome. There are also technological challenges that must be addressed.
A key issue for operators is how to provide the backhaul capacity needed to support ever-growing data traffic. Of the numerous solutions available, microwave backhaul is seeing increased popularity amongst operators as it can be installed faster and at a lower cost than fibre and cable solutions.
The self-backhauling mesh network is another solution getting attention. Unlike traditional networks that connect base stations from a central point, base stations in a mesh network are connected to each other as well as a central point, extending network reach considerably.
Self-backhauling systems can also reduce network congestion with capacity scaled up and down as required.
In order to keep up with the rising demands on their networks, operators are increasingly deploying conventional macro and newer small-cell base station links. This in turn puts greater pressure on backhaul throughput. As a result, more microwave backhaul links are being deployed in networks, resulting in a higher risk of signal interference in congested areas.
As a result of these challenges, operators are investigating various technologies and solutions to ensure that networks can provide the high-capacity, ubiquitous coverage that subscribers are coming to demand and mobile services will increasingly rely on.
To keep up with the rapid growth in data capacity demands, many cell sites have been split and new cells added. Over 95% of all capacity gains in cellular networks have been achieved by either sector splitting or adding new cell sites, both of which increase cell density.
Today in the macro environment, additional sectorisation is being carried out by upgrading sites from three sectors to six sectors and using advanced optimisation solutions. While this natural trend has clearly driven the industry forward, further capacity additions are constrained due to the physical limitations of additional space for sites and concerns that this may cause interference.
Due to the limitations of sector splitting, operators are investigating solutions that combine multiple technologies. One example is heterogeneous networks (or HetNets), which relates to network deployments that encompass multiple base station types, as opposed to macro-only cell deployments.
HetNets will play a crucial role in 4G deployments since they can utilise multiple technologies to provide a seamless 4G experience. The premise of HetNets is to seamlessly combine micro and macro networks to ensure ubiquitous coverage and capacity, with the macro network providing the coverage range, while the micro network provides capacity for usage hotspots. The former is served by a high power base station providing broad coverage, while the latter is made up of multiple lower power technologies, designed to cover limited areas, such as office blocks or shopping centres.
The micro networks consist of multiple low power technologies such as picocells, microcells, distributed antenna systems (DAS) and wireless LANs, which can support a very high capacity of data traffic. Meanwhile, the operator’s core cellular network – the macro network – delivers widespread, lower capacity coverage. The big advantage for operators is that HetNets allow for a much higher quality of coverage at a much lower cost than rolling out universal high capacity coverage.
This approach allows operators to build-up their micro network to reinforce high usage hotspots whilst simultaneously expanding the network to eliminate blind spots. Wireless LANs can also be incorporated into the HetNet to converge mobile and fixed-line networks, helping to relieve traffic congestion on the core mobile network.
We have already seen several different frequencies used in today’s active 4G networks, ranging from 800MHz to 2.6GHz. This variation, coupled with the prospect of new frequencies being refarmed in the future, makes it essential for operators to ensure that both the coverage and capacity networks can support multiple frequencies. It’s equally important for the infrastructure to support multiple operators, enabling certain carriers to share implementation costs.
Active and integrated antennas
Increasingly, radio sections of the base station are being integrated into the antenna instead of the remote radio head (RRH). Here, operators can choose from integrated antennas or active antennas. An integrated antenna is simply where the RRH is integrated into the base station antenna enclosure. In this case the jumpers between the RRH and the antenna are removed. Generally there are no major performance benefits, however, they are more compact. Active antennas on the other hand can enable several new radio features.
Active antennas are likely to be a key technology in next generation mobile networks and we expect 10% of base station antennas to use them by 2015. As with integrated antennas, they take all the functionality of the traditional RRH and integrate it into the antenna housing. The difference is that the radio section is separated into several radios that each drive an individual antenna element, instead of a single 60W RF amplifier driving all the antenna elements in parallel.
Active antennas provide operators with the means to support larger volumes of subscribers (and thus generate more revenue) by enabling them to sectorise coverage areas vertically. With active antennas, operators can take a sector, split it vertically, and come close to doubling its capacity – improving the service for subscribers and generating more revenue.
Another key benefit of active antennas is their ability to provide ‘graceful degradation’. Currently, if the RRH fails, the sector it covers goes down, impacting revenue and service levels until it is repaired. Operators are also compelled to send a repair crew to the site immediately.
With graceful degradation the problem is less urgent as there are multiple amplifiers/radios as opposed to just one. This lowers the operator’s expenditure and ensures service levels remain high even when network hardware fails. This is taken a stage further by the ability of active antennas to ‘self-heal’. If one element of the antenna fails, intelligent systems can automatically redistribute the power to the remaining elements to maintain the quality of the radio coverage.
Active antennas can also be set to angle their ‘transmit and receive’ beams in different directions. Thus they can collect energy on the uplink from the edge of the cell, while transmitting less energy into the adjacent cell by adjusting where those beams are, so the system sees far more uplink throughput. As active antennas will also lower the number of pieces of equipment that need to be mounted to a base station, they should lower the total cost of each site in the long-term.
As with any exciting and industry-changing technology, there are always going to be obstacles to overcome. However, operators should not let this dampen their enthusiasm for 4G. There are a great many technologies readily available, which can help them to conquer any challenges that arise and successfully rollout 4G. By taking the time to prepare their networks now, operators can make sure they are ready to go live with 4G after next year’s 4G spectrum auction.